By Lightimes Editor, Scott McMahan
The U.S. Department of Energy (DOE) released the CALiPER Report 24, which discusses the performance and accelerated lifetime testing of OLED luminaires. The report is the first CALiPER report that discusses the independent procurement and evaluation OLED luminaires.
As expected, OLED luminaires have a long way to go before they catch up with the performance, efficacies, and lifetimes of current LED luminaires. The report notes that currently there is not an accepted standard specifically for accelerated life testing of OLED luminaires. A new standard would have to reveal all potential failure methods in OLEDS, which so far are partially unknown. However, the DOE was able to conclude that OLED lifetimes and efficiencies are far below that of conventional LEDs currently on the market.
PNNL laboratories conducted most of the testing and RTI performed the stress testing.
Among the OLED luminaires tested, the overall efficacy was found to be considerably lower than contemporary LED luminaires. The efficacy ranged from as low as 23 lumens per watt (LPW) up to 45 LPW. According to data from the OLED panel manufacturers, the LPW ranged between 42 and 55. The CALiPER testing found that much of this efficacy reduction is due to very inefficient driver and transformer selections and combinations.
The report pointed out that the wider availability of dedicated OLED drivers should improve OLED light efficacies in the near future.
The drivers for all four CALiPER OLED luminaire types were different. Some OLED luminaires used a single driver and others used a combination of electronic components for voltage transformation, conversion from AC to DC, and voltage/current control.
The testing found that the OLED luminaires performed very closely to the manufacturers’ published technical data, where available. Also, all of the tested products provided a soft, diffuse light with a roughly Lambertian emission.
Unlike LED lighting technology which is now in a mature stage of development, the DOE report says that OLED panels, drivers, and transformers are still in a steep curve of development. Much improvement is required before the technology can reach a mature stage.
The goals of OLED developers include improving lifetimes, efficacy, lumen maintenance, and color quality. Other technological goals include developing a broader range of color temperature options for OLEDs and producing higher efficiency drivers. Along with the improvements in lifetime, developers are working on enhancing OLED robustness and resistance to high temperatures, high humidity, and rough handling.
OLED lighting is really in its infancy in terms of its development and adoption. Improvements in its performance and longevity are only part what will make it into a mature technology. The greater involvement of industry and academia in the development effort would be needed to make OLEDs an economically sensible choice. I don’t see that happening anytime soon.
Additionally, the industry has to get together to create standards for accelerated longevity testing. While the testing standard that the study used, LM-79 08, was developed for LEDs, it would have to be modified for OLEDs, and not all of the potential long-term failure modes are even known.
While the DOE says that such improvements could make OLEDs a trusted solution for architectural lighting, a considerable amount of development work and performance improvements are needed before OLEDs can mature as a technology.
